I have a laptop that came with Windows XP. I upgraded to Windows 7 when it came out, and am planning on selling the laptop. Unfortunately, I think the Windows 7 upgrade disc got accidentally thrown out when I was throwing some old software out.

I was planning on doing "Darik's Book and Nuke" to wipe everything, but then I would have no way to get Windows 7 back on it legally. Is there any way I can restore Windows 7 to a clean install, and then "wipe unused space" with a disk utility to protect my information?

I do have the Windows XP factory restore disc that came with the laptop, but it will obviously sell easier and probably for more with Windows 7 on it.

Also, as long as you have the valid key/license, you are free to use copies of disks you obtained from a 'less than reputable' source. It's not the best idea (and usually doesn't sell well), and MS might not support you (or your customer) if you call them with a problem installing from it.

Only a half answer, really, but Eraser can easily wipe the free unused space on your disk. You can even customize it beyond the default 1-pass of random data if you're really paranoid, but that's not necessary at all. I use it regularly in just this fashion, on Windows 7 no less.

Eraser can also securely erase files, so you can delete all your user data, program files, empty the temporary directory, etc. in a secure fashion. Of course, that's redundant if you're going to wipe the free space anyway...

Unfortunately, I don't know how to restore Windows 7 to a clean start, other than by painstakingly deleting everything manually (and then wiping the free space). Neither easy nor trivial, I know, but only method I know of.

Since you do not have the original disk, I suggest you use the "System Restore" feature, and go back as far as possible with it. Remove all your documents, then delete your user account. Make a new one with no password and just the name "User" or something generic.

Then head over to "Programs and Features", and remove every single program. Leave drivers for the laptop though, if it has touchpad or other hardware drivers.

This may be time consuming, but without a disk its rather difficult to do it legally.